# std::num_get

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< cpp‎ | locale

Defined in header `<locale>` |  |
template< class CharT, class InputIt = std::istreambuf_iterator<CharT> > class num_get; |  |

Class `std::num_get` encapsulates the rules for parsing string representations of numeric values. Specifically, types bool, unsigned short, unsigned int, long, unsigned long, long long, unsigned long long(since C++11), float, double, long double, and void* are supported. The standard formatting input operators (such as cin >> n;) use the `std::num_get` facet of the I/O stream's locale to parse the text representations of the numbers.

Inheritance diagram

If a `std::num_get` specialization is not guaranteed to be provided by the standard library (see below), the behaviors of its get() and do_get() are not guaranteed as specified.

### Specializations

The standard library is guaranteed to provide the following specializations (they are required to be implemented by any locale object):

Defined in header `<locale>`
std::num_get<char> | creates narrow string parsing of numbers
std::num_get<wchar_t> | creates wide string parsing of numbers

In addition, the standard library is also guaranteed to provide every specialization that satisfies the following type requirements:

- `CharT` is one of
  - char,
  - wchar_t, and
  - any other implementation-defined character container type that meets the requirements for a character on which any of the iostream components can be instantiated; and
- `InputIt` must meet the requirements of LegacyInputIterator.

### Nested types

Type | Definition
`char_type` | `CharT`
`iter_type` | `InputIt`

### Data members

Member | Description
std::locale::id `id` [static] | the identifier of the facet

### Member functions

(constructor) | constructs a new `num_get` facet (public member function)
get | invokes `do_get` (public member function)

### Protected member functions

(destructor) | destructs a `num_get` facet (protected member function)
do_get [virtual] | parses a number from an input stream (virtual protected member function)

### Example

Run this code

    #include <iostream>
    #include <iterator>
    #include <locale>
    #include <sstream>
    #include <string>

    int main()
    {
        std::string de_double = "1.234.567,89";
        std::string us_double = "1,234,567.89";

        // parse using streams
        std::istringstream de_in(de_double);
        de_in.imbue(std::locale("de_DE.UTF-8"));
        double f1;
        de_in >> f1;

        std::istringstream us_in(de_double);
        us_in.imbue(std::locale("en_US.UTF-8"));
        double f2;
        us_in >> f2;

        std::cout << "Parsing " << de_double << " as double gives " << std::fixed
                  << f1 << " in de_DE locale and " << f2 << " in en_US\n";

        // use the facet directly
        std::istringstream s3(us_double);
        s3.imbue(std::locale("en_US.UTF-8"));

        auto& f = std::use_facet<std::num_get<char>>(s3.getloc());
        std::istreambuf_iterator<char> beg(s3), end;
        double f3;
        std::ios::iostate err;
        f.get(beg, end, s3, err, f3);

        std::cout << "parsing " << us_double
                  << " as double using raw en_US facet gives " << f3 << '\n';
    }

Output:

    Parsing 1.234.567,89 as double gives 1234567.890000 in de_DE locale and 1.234000 in en_US
    parsing 1,234,567.89 as double using raw en_US facet gives 1234567.890000

### Defect reports

The following behavior-changing defect reports were applied retroactively to previously published C++ standards.

DR | Applied to | Behavior as published | Correct behavior
--- | --- | --- | ---
LWG 427 | C++98 | `num_get` was guaranteed to accept any `CharT` that meets the requirements for a character on which any of the iostream components can be instantiated | only guarantees to accept char, wchar_t and other implementation- defined character types
LWG 2392 | C++98 | only character type `CharT` could be guaranteed to be accepted by `num_get` | can guarantee to accept implementation- defined character container types

### See also

numpunct | defines numeric punctuation rules (class template)
num_put | formats numeric values for output as character sequence (class template)
operator>> | extracts formatted data (public member function of `std::basic_istream<CharT,Traits>`)

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